1. Field of the Invention
The present invention relates generally to truck and/or trailer mounted portable devices for dispensing pavement repair materials and, specifically, to such a portable device for dispensing repair materials for asphalt pavements.
2. Description of the Prior Art
In the past, as many as three vehicles were sometimes needed to repair openings and potholes in asphalt, concrete and other roadway surfaces. One vehicle provided an air compressor for use with various pneumatic repair tools which were used to dress the hole, crack or cavity to be filled. Another vehicle contained liquid asphalt tack material which would be sprayed into the dressed cavity, and a third vehicle would deliver asphalt mix material to the cavity. The asphalt would then be packed, compacted and leveled by hand to complete the repair.
U.S. Pat. No. 4,196,827, issued Apr. 8, 1980, entitled xe2x80x9cPortable Machine For Transporting Heated Asphalt Products For Use In Repair Asphalt Pavementxe2x80x9d shows a portable machine which was designed to incorporate all phases of the pavement repair into one mobile unit. The machine has a hopper for transporting asphalt mix, and a reservoir below the hopper having a heat source. The reservoir contained liquid asphalt tack material. The heat source is used to heat the liquid tack material, and the tack material is used to heat the asphalt mix in the hopper by heat transfer. Asphalt tack material is also dispensed from the tack material tank by means of spray equipment connected to a discharge valve on the rear of the truck.
In spite of being less expensive to operate in terms of material and labor, the previously described device possessed several different disadvantages. For example, the liquid asphalt tank carried on the unit was suitable for road oils and cutbacks but was not well suited for use with asphaltic cements. Also, in the case of the device described in the ""827 patent, the liquid asphalt tank was not suited for use with asphalt emulsions, because the volatile contents of the emulsions would be driven off and dry out the materials.
U.S. Pat. No. 4,944,632, issued Jul. 31, 1990, and assigned to the assignee of the present invention showed a portable unit with a separate tack oil tank which was provided with its own heat source and which was designed to prevent phase separation of the tack oil materials to overcome some of the deficiencies of the prior art devices. This tank could be used successfully with both emulsions and asphalt cutback oils.
Both of the prior art devices utilized a liquid heat transfer medium to heat the asphalt hopper of the device and maintain the asphalt mix materials therein in a workable state. While a liquid heat transfer medium has been used successfully for many years to heat the asphalt hopper, there are disadvantages associated with the use of a liquid medium. Many of these disadvantages relate to the release of volatile components of the medium as it is repeatedly heated during use. The liquid medium must also be maintained and/or replaced at regular maintenance intervals.
Accordingly, it is an object of the present invention to replace the liquid heat transfer medium used in the prior art to heat the hopper compartment of an asphalt repair apparatus with a dry, radiant heat source which does not require refill and which does not emit volatile organic emissions to the atmosphere.
Another object of the invention is to provide such a dry, radiant heat source for an asphalt repair apparatus which heat source safely and effectively heats the asphalt repair materials without hardening, burning or charring such materials.
Another object of the invention is to provide a means for retaining heat from the dry, radiant heat source within the device of the invention, limiting heat loss when the heat source is not operating.
Another object of the invention is to provide such an apparatus which is simple in design and economical to manufacture.
The portable apparatus of the invention is used to transport heated pavement repair materials for use in repairing roadways and other traffic bearing surfaces. The device includes a body adapted to be mounted on a portable base for transporting the body to a repair site. The body has a hopper compartment with a V-shaped bottom wall for transporting asphalt mix material and a generally V-shaped heating chamber located below the hopper compartment. The V-shaped bottom wall of the hopper compartment defines an upper extent of the heating chamber. A screw conveyor is mounted in the bottom of the hopper compartment for dispensing asphalt mix materials therefrom. An agitator, such as a paddle shaft, is located above the screw conveyor in the hopper compartment for agitating the hopper materials. A dry heat means is associated with the heating chamber for heating the chamber and for transferring heat to the hopper compartment through the hopper bottom wall to maintain the asphalt mix materials in a workable state.
Preferably, the V-shaped bottom wall of the hopper compartment forms an upper, uninsulated common wall with the heating chamber. The heating chamber also has oppositely extending, insulated bottom wall portions. In a preferred embodiment of the invention, the dry heat means comprises a pair of oppositely arranged retort tubes located within the heating chamber on either side of the V-shaped bottom wall of the hopper. The retort tubes are heated by a thermostatically controlled gas burner for supplying dry, radiant heat to the bottom wall of the hopper. Each retort tube forms a single pass loop which has a burner installed at one extent thereof and which communicates with an exhaust stack at the opposite extent thereof. In a preferred arrangement, each retort tube is provided in the shape of an inclined U arranged in a plane which is generally parallel to a selected one of the oppositely extending, insulated bottom wall portions of the heating chamber. Each retort tube has a pair of outlets to the exterior of the tank, one of the outlets having the burner mounted therein and the other of the outlets being connected to the exhaust stack.
A damper system is installed in the exhaust stacks for limiting heat loss from the heating chamber. A damper in each exhaust stack remains in the open position while the burners are operating to provide adequate air flow for the burners. A control system monitors an output signal from a thermostat mounted in the heating chamber, and, when the heating chamber has reached a desired temperature, the control system turns off the burners and actuates a solenoid that moves the dampers to a closed position. This prevents heated air from flowing out of the exhaust stacks, retaining heat within the heating chamber.